Automatic clasp for wristwatch strap

ABSTRACT

A clasp and a production method thereof. The inventive clasp includes at least one main element ( 1 ) and at least one element ( 3 ) which pivots in relation to the main element. The clasp is characterised in that each of the aforementioned elements ( 1, 3 ) includes two longitudinal arms which are rolled up to form a hinge ( 7, 15 ). Moreover, at least one of the ends of one of the elements ( 1, 3 ) includes a flexion spring ( 11 ) which can rest against the other element ( 3, 1 ) for the elastic support thereof and each arm ( 5, 13 ) of the main element ( 1 ) and the pivoting element ( 3 ) is provided with at least one longitudinal stiffening rib ( 20, 22 ).

The present invention relates to a clasp of the automaticopening/closure type, particularly for wristwatch strap.

Numerous types of clasps are known, which are essentially constituted bytwo elements mounted to pivot with respect to each other, at therespective ends of which the two free ends of the straps constituting awristwatch are connected. The two elements forming such a clasp are thusadapted to occupy two positions, namely a first position, or position ofclosure, in which the two elements are locked on each other bymechanical holding means, and a second position, or position of opening,in which these two elements are released, thus at the same timeincreasing the overall diameter of the wristwatch so as to allow theuser to easily introduce it on or remove it from his/her wrist.

One drawback inherent in this type of clasp comes from the fact that thedevices for locking the two elements which constitute it, either requirea considerable effort to ensure locking thereof, or present the risk ofnot holding the watch strap in complete safety.

In order to avoid this type of drawback, a clasp has been proposed inPatent Application FR-A-2 710 503, in which the two elements arestressed, in position of closure, by elastic means which thuspermanently ensure a force tending to maintain the clasp in position ofclosure. Such a clasp makes it possible to limit the risks of untimelyopening of the watch strap.

One drawback of this type of clasp is that, in position of opening, thetwo elements cannot pivot beyond an angle of 180°, this sometimesrendering it difficult to introduce the user's wrist in the watch strap.Moreover, any effort of opening exerted on these two elements, whichtends to cause them to pivot beyond an aligned position, has the effectof irreparably deteriorating the clasp.

This is why a clasp of the aforementioned type has been proposed inPatent EP-A-0 867 132, in which the two elements are respectivelyconstituted by a main element and a pivoting element, the main elementcomprising a flexion spring stressing an elongation of the pivotingelement beyond the articulation, in two stable positions of equilibrium,namely a first position, or position of closure, in which it applies thepivoting element on the main element, and a second position, or positionof opening, in which it moves the two elements apart from each other,the pivoting element comprising at least one slot adjacent to thearticulation, whose dimensions are such that they allow the flexionspring, when the pivoting element is in the position of opening, totraverse this slot so as no longer to stress said pivoting element.Furthermore, in certain forms of embodiment, the system is one withdouble development, i.e. the clasp is composed of three elements, namelya main element which comprises at each of its ends an articulation onwhich a pivoting element is mounted as described previously.

The clasps produced in this way are constituted by pieces machined inthe mass and, by reason of the fact that their different constituentelements must respond to contradictory mechanical contraints, they aremade of a plurality of assembled pieces. For example, the flexion springis added by fixation means, such as riveting or welding, on the mainelement. These different contraints lead to the clasps made in this wayusually being intended to equip very high quality wristwatch straps, andthis due to their particularly high cost price.

The present invention has for its object to propose a clasp of theaforementioned type intended to be manufactured, not by mechanicalmachining processes, but by processes for producing pieces of smallthickness, such as stamping, folding and cutting out.

The invention also proposes a clasp of this type in which the springwith which the main element is provided forms an integral part of thelatter and is not constituted by an added piece. The present inventionthus makes it possible to produce a clasp of high mechanical quality ata particularly attractive cost price.

According to the invention, it is thus proposed to produce a mainelement and a pivoting element which are constituted from a thin foil ofstainless steel. Now, it is known that, in the domain of wristwatchstraps, the so-called stainless steels are subjected to oxidationstresses which are particularly high, so that very few of these steelsprove in reality to be effectively stainless.

However, professionals in these techniques are acquainted withcompletely stainless steels, even under the particularly severeconditions mentioned previously. However, such steels present, moreover,drawbacks and particularly that of being particularly difficult tomaster concerning their characteristics of hardness and of elasticity.In effect, these steels are not sensitive to quench hardening, and theirhardness is acquired by successive operations of die work or of rolling,which are effected from a sample of steel whose thickness is muchgreater than that of the final piece. Although such contraints have onlyan accessory importance when it is proposed to make pieces machined inthe mass, they prove particularly awkward when it is question of piecesmade from a strip of stainless steel.

Another difficulty resides in the fact that the two elementsconstituting the clasp, namely the main element and the pivotingelement, are formed by parts which must imperatively present verydifferent characteristics of stiffness, since one zone of these elementsmust be sparingly elastic and sparingly hard in order to be able to berolled so as to constitute the hinges for receiving the pivot pins,another zone must have a sufficient stiffness to constitute a springblade making it possible to create the elastic force ensuring that theclasp is held in position of use, and finally a third zone must be rigidin order to counterbalance the stiffness of the spring.

The present invention has for its object to propose a method ofmanufacture making it possible to produce each of the two elementsconstituting a clasp, in one piece.

The present invention thus has for its object a method for manufacturinga clasp, particularly for wristwatch strap, from a metal strip, of thetype comprising a main element and at least one pivoting element, whichare connected at one of their respective ends by an articulation, aflexion spring fast with one of these elements being applied, at leastin position of closure, on the other element in order to hold itelastically in this position of closure, characterized in that itcomprises the steps consisting in:

-   -   using a strip whose stiffness is the one desired for the spring,    -   making, by cut-out, a blank of each of these elements, so as to        form on each of them at least two longitudinal arms, and on the        main element two recesses inside the two arms forming between        the two arms a central flexion spring,    -   subjecting these arms to an annealing exclusively at their ends        so as to allow rolling thereof,    -   increasing the stiffness of these arms by making at least one        rib along the longitudinal axis thereof.

In a first form of embodiment of the invention, the method comprises astep during which a blank band is constituted from a strip constitutedby a wound band, of which the width corresponds to one of the dimensionsof the element to be produced, each of the blanks constituting the blankband being connected to the blanks which are adjacent thereto by atleast one connecting tab. The blanks may be disposed so that theirlongitudinal axis is oriented perpendicularly to the longitudinal axisof the blank band.

In a step of the method, the blank band will advance, along itslongitudinal axis, in front of localized heating means in zones disposedon its transverse edges, so as to effect an operation of annealing on atleast one longitudinal band of the blank band. The localized heatingmeans will preferably be constituted by a laser beam.

According to the invention, an operation of rolling will be effected atthe end of the arms of the elements, after the heating phase, so as toconstitute hinges.

Likewise, two arms of the same end of a pivoting element will be woundso as to constitute a double hinge, namely an inner hinge intended toreceive a pivot pin common with the main element and an outer hingeintended to receive a stop pin.

Furthermore, once the end of the arm is wound, the end of the arm may bewelded on the element on which it is constituted.

Although for the localized heating operations it is possible to employvarious processes, it has been observed that welding by laser beam madeit possible to obtain results which are particularly noteworthy by itsprecision.

The present invention also has for its object a clasp, particularly forwristwatch strap, of the type comprising at least two elements, namely amain element and a pivoting element which is mounted to pivot withrespect to the latter by means of an articulation, characterized inthat:

-   -   each of these elements comprises at at least one of its ends two        longitudinal arms whose ends are rolled up so as to constitute a        hinge of said articulation,    -   at least one of the ends of one of the elements comprises a        flexion spring adapted to come, at least in position of use, in        abutment against the other element so as to ensure elastic        support thereof,    -   each arm of the main and pivoting elements is provided with at        least one longitudinal stiffening rib.

The flexion spring will preferably be formed on the main element.Furthermore, the rolling of the arms of that of the two elements whichis not provided with the flexion spring may be double, so as to form, onthe one hand, a first inner hinge admitting the pivot pin traversing thehinges of the articulation, and a second outer hinge intended to supporta stop pin disposed beyond the first pivot pin, towards the outside, andon which the flexion spring will come into abutment when the clasp is inposition of use.

In a particularly interesting form of embodiment of the invention, atleast the element provided with the flexion spring will be constitutedby a stainless steel having a high content of elements such as nickel,chromium, molybdenum, cobalt, the sum of the contents of these elementsbeing greater than 80%.

A form of embodiment of the present invention will be describedhereinafter by way of non-limiting example, with reference to theaccompanying drawings, in which:

FIG. 1 is a plan view of the blanks constituting the main and pivotingelements of an example of clasp according to the invention.

FIG. 2 is a view in perspective of a main element and of a pivotingelement before they are assembled on a clasp of double-development type.

FIG. 3 is a view in perspective of the double-development clasp shown inFIG. 2, the elements constituting the latter being assembled and one ofthe pivoting elements being in position of opening.

FIG. 4 is a view in perspective of the clasp shown in FIGS. 2 and 3, thetwo pivoting elements being in position of closure.

FIG. 5 is a schematic view in elevation of an example of installationallowing a clasp according to the invention to be manufactured.

FIG. 6 is a schematic plan view of a blank band in the course of theprocess of manufacture.

The clasp according to the invention which is shown in FIGS. 2 to 4 isof the double-development type, i.e. it is constituted by threeessential elements, namely a main element 1 and two pivoting elements 3.

FIG. 7 is a view in perspective of a variant embodiment of a claspaccording to the invention.

The main element 1 is curved and terminates at each of its two ends bytwo arms 5 of which the ends are wound so as to constitute hinges 7.These ends comprise two longitudinal notches 9 which thus define acentral tongue which constitutes a flexion spring 11.

The pivoting element 3 likewise comprises, on one side, two longitudinalarms 13 which terminate by a double hinge 15, formed by an inner hinge15 a and an outer hinge 15 b, and which are so disposed, in thetransverse direction, that they can be positioned in the longitudinalnotches 9 of the main element 1. It comprises at its other end a centraltab 6 whose end is rolled so as to produce a hinge 8 intended to beconnected to one of the ends of the strap of the wristwatch.

The main (1) and pivoting (3) elements are connected by a pivot pin 16which is fitted by force in the hinges 7 of the main element 1 and theinner hinges 15 a of the pivoting element 3. A stop pin 18 isforce-fitted in the hinges 15 b.

When the clasp is in position of closure, in other words in position ofuse, as shown in FIG. 4, the flexion springs 11 are in abutment on theirrespective stop pins 18, so that they exert thereon a force creating atorque on the pivoting elements 3 (by reason of the stagger e existingbetween the pivot pin 15 and the stop pin 18) tending to apply themelastically against the main element 1, so that they then ensure theelastic support in closed position of the clasp.

The arms of the main (1) and pivoting (3) elements will preferably beprovided with respective ribs 20 and 22 which will allow their rigidityto be controlled.

When the user wishes to remove the wristwatch, he/she pivots the mainelement and pivoting element of the clasp to bring the latter into theposition shown in FIG. 3 and, as soon as the two main (1) and pivoting(3) elements are substantially in line with each other, the flexionspring 11 ceases to be in abutment on the stop pin 18, with the resultthat, in that case, it no longer exerts a torque on the pivoting element3.

When, as in the form of embodiment shown in the Figures, the spaceincluded between the arms 13 of the pivoting element 3 extends inwardlyto constitute a window 24 whose dimensions are greater than those of theend of the spring 11, it is then possible to pivot the two elements to agreater extent, since, during this movement, the end of the spring 11has the possibility of traversing the window 24.

Each of the main (1) and pivoting (3) elements is obtained from a stripof stainless steel which is cut out, for example by a stampingoperation, so as to constitute two respective blanks 1′ and 3′, as shownin FIG. 1.

According to the invention, the strip presents a rigidity which is equalto that which it is desired to give the flexion spring 11, in order thatthe latter be in a position to perform its functions as specifiedpreviously.

The hinges 7 and 15 of the main (1) and pivoting (3) elements are formedby winding the ends of the respective arms 5 and 13 and welding the endsof the latter on the corresponding elements. This welding operation willpreferably be effected with the aid of means allowing an extremeprecision and in particular by means of the laser beam type.

However, for such a rolling to be possible, it is necessary that atleast those parts of the arms 5 and 13 which will be wound, i.e. theirends, present a slight stiffness and this is why, prior to the windingoperation, the ends of these arms will be heated so as to subject themto annealing. This operation will have to be very localized in order notto lessen the mechanical qualities of the other parts of the blanks, andmeans of the laser beam type will be employed to that end.

Manufacture of the main (1) and pivoting (3) elements will preferably beeffected by a continuous process in which the blanks are arranged in acontinuous band (or blank band 12), each blank being connected to theblanks which are adjacent thereto by connecting tabs 4.

Such an example of implementation of the invention will be describedhereinafter, of which certain of the steps are represented in FIGS. 5and 6. In this example of implementation, the blanks 1′ and 3′ aredisposed transversely with respect to the metal strip, i.e. theirlongitudinal axis xx′ is perpendicular to the longitudinal axis yy′ ofthe strip.

FIGS. 5 and 6 shows the different successive phases of the processallowing the main element 1 of the clasp to be made from a rolled upstrip 2 which unwinds all along the process and advances in front ofdifferent work stations P₁, P₂, . . . , P₅, corresponding respectivelyto machining steps I, II, . . . , V.

In the first step I, the strip 2 passes in the cut-out station P₁ wherethe blank 1′ is formed, this cut-out being such that the blank isconnected to each of the blanks 1′ which are adjacent thereto by twoconnecting tabs 4 so as to form a blank band 12, so that it is possibleto maintain all along the chain the advantages associated with this typeof arrangement.

During the second step II, the blank band 12 moves in front of stationP₂ which is constituted by a laser beam which effects a very localizedheating on the two longitudinal edges of the strip which corresponds tothe two ends of the blank 1′ and more precisely to the ends of the arms5. The width l of this treated band 10 (shown double-hatched in FIG. 6),corresponds to the length l of the arms which will subsequently berolled up to make the hinge 7. This length will be limited so as not toreduce the stiffness of the flexion spring 11. The person skilled in theart will know how to adjust the power of the tool as well as the speedof advance of the blank 1′ in front of the latter so that the metal istaken to the appropriate temperature to effect an efficient annealing.

In the course of the third step III, the ends of the arms 5 are rolledup so as to form the hinges 7, at the two ends of the blank 1′. When theproduction chain will manufacture the pivoting elements 3, double hingeswill be produced at one of the ends thereof, i.e. they will beconstituted by a rolling slightly flattened at its centre which willenable it to receive, on the inner hinge 15 a, the pivot pin 16 and, onthe outer hinge 15 b, the stop pin 18.

In the course of the fourth step IV, a rib is made, at station P₄, oneach of the arms of the pivoting element 3 which will make it possibleto compensate its loss of rigidity provoked by the annealing operation.

By these various operations, each part constituting these elements isgiven the inherent rigidity which is necessary for it to ensure correctfunctioning and appropriate reliability of the clasp.

In the course of the fifth and last step V, at station P₅, a cut-outmachine is employed for shearing and eliminating the connecting tabs 4which join the blanks 1′ together.

More or fewer than two connecting tabs 4 might, of course, be used inaccordance with the invention.

The clasps according to the invention may be made with numerous types ofmetals. However, in the domain of clasps intended for time-keepingproducts, preference will be given to a stainless steel with highcontent of elements such as nickel, chromium, molybdenum, cobalt, thesum of the contents of these elements preferably being greater than 80%,by reason of its real and recognized qualities of inoxydability inhighly oxydizing environments, such as those to which these products aresubjected when they are in contact with users' wrists.

Although the example of clasp described is of the type with doubledevelopment, the present invention is, of course, equally wellapplicable to a clasp of the type with single development which, in thatcase, would comprise only one pivoting element 3.

As shown in FIG. 7, it might, of course, be possible to effect akinematic reversal of the support of the flexion spring by making thelatter on a pivoting element, and the window 24 on the main element.

1. Method for manufacturing a clasp, particularly for wristwatch strap,from a metal strip (2), of the type comprising a main element (1) and atleast one pivoting element (3), which are connected at one of theirrespective ends by an articulation, a flexion spring (11) fast with oneof these elements (1, 3) being applied, at least in position of closure,on the other element (3, 1) in order to support it elastically in thisposition of closure, characterized in that it comprises the stepsconsisting in: using a strip (2) whose stiffness is the one desired forthe spring (11), making, by cut-out, a blank (1′, 3′) of each of theseelements (1, 3), so as to form on each of them at least two longitudinalarms (5), and on the main element (1) two recesses (9) inside the twoarms (5) forming therebetween a central flexion spring (11), subjectingthese arms (5, 13) to an annealing exclusively at their ends so as toallow rolling thereof, increasing the stiffness of these arms (5, 13) bymaking at least one rib (20, 22) along the longitudinal axis thereof. 2.Method according to claim 1, characterized in that it comprises a stepduring which a blank band (12) is constituted from a strip constitutedby a wound band (2), whose width corresponds to one of the dimensions ofthe element to be made, each of the blanks (1′, 3′) constituting theblank band (12) being connected to the blanks which are adjacent theretoby at least one connecting tab (4).
 3. Method according to claim 2,characterized in that the blanks (1′, 3′) are disposed so that theirlongitudinal axis (xx′) is oriented perpendicularly to the longitudinalaxis (yy′) of the blank band (12).
 4. Method according to claim 1,characterized in that the blank band (12) advances, along itslongitudinal axis (yy′), in front of localized heating means (P₂) inzones (10) disposed on its transverse edges, so as to effect anoperation of annealing on at least one longitudinal band (10) of theblank band (12).
 5. Method according to claim 1, characterized in thatthe localized heating means are constituted by a laser beam generator(P₂)
 6. Method according to claim 1, characterized in that, after theheating phase (II), an operation of rolling (III) is effected at the endof the arms of the elements, so as to constitute hinges (5, 7, 15, 8).7. Method according to claim 6, characterized in that two arms (13) ofthe same end of a pivoting element (3) are wound so as to constitute adouble hinge (15), namely an inner hinge (15 a) intended to receive apivot pin (16) common with the main element (1) and an outer hinge (15b) intended to receive a stop pin (18).
 8. Method according to claim 6,characterized in that it comprises a step consisting in welding the endof the arm, once the latter is wound, on the element on which it isconstituted.
 9. Method according to claim 7, characterized in that thiswelding is effected by a laser beam generator.
 10. Method according toclaim 1, characterized in that it comprises a step (IV) after theannealing operation (II), in the course of which longitudinal stiffeningribs (20, 22) are made on the arms (5, 13) of the main (1) and pivoting(3) elements.
 11. Method according to claim 1, characterized in that itcomprises a last phase (V) during which the tabs (4) for connection ofthe elements are eliminated.
 12. Clasp, particularly for wristwatchstrap, of the type comprising at least two elements, namely a mainelement (1) and a pivoting element (3) which is mounted to pivot withrespect to the latter by means of an articulation, characterized inthat: each of these elements (1, 3) comprises at at least one of itsends two longitudinal arms (5, 13) whose ends are rolled up so as toconstitute a hinge (7, 15) of said articulation, at least one of theends of one of the elements (1, 3) comprises a flexion spring (11)adapted to come, at least in position of use, in abutment against theother element (3, 1) so as to ensure elastic support thereof, each arm(5, 13) of the main (1) and pivoting (3) elements is provided with atleast one longitudinal stiffening rib (20, 22).
 13. Clasp according toclaim 12, characterized in that the flexion spring (11) is formed on themain element.
 14. Clasp according to claim 12, characterized in that therolling of the arms (13) of that of the two elements which is notprovided with the flexion spring (11) is double, so as to form, on theone hand, a first inner hinge (15 a) admitting the pivot pin (16)traversing the hinges of the articulation, and a second outer hinge (15b) intended to support a stop pin (18) disposed beyond the first pivotpin (16), towards the outside, and on which the flexion spring (11)comes into abutment when the clasp is in position of use.
 15. Claspaccording to claim 12, characterized in that the ends of the armsforming the hinges are connected by welding to each element on whichthey are formed.
 16. Clasp according to claim 12, characterized in thatat least the element provided with the flexion spring (11) isconstituted by a stainless steel having a high content of elements suchas nickel, chromium, molybdenum, cobalt, the sum of the contents ofthese elements being greater than 80%.